Multiplexer, transmission device, and reception device

ABSTRACT

A multiplexer includes filters, a common terminal with which an inductance element is connected to a connection path of the common terminal and an antenna element and a capacitance element is connected in series to the connection path, and another inductance element. An input terminal of one of the filters is connected to the common terminal via the another inductance element, and is connected to a parallel resonator. In each of the filters other than the one filter, one of the input terminal and the output terminal, which is a terminal closer to the antenna element, is connected to the common terminal, and is connected to the series resonator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2017-031779 filed on Feb. 23, 2017. The entire contentsof this application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multiplexer including an elastic wavefilter, a transmission device, and a reception device.

2. Description of the Related Art

In recent years, there has been a demand for cellular phones to be ableto handle multiple frequency bands and multiple wireless formats with asingle terminal, i.e., to have multi-band and multi-mode capabilities.To this end, a multiplexer is disposed immediately beneath a singleantenna, to demultiplex high-frequency signals having multiple wirelesscarrier frequencies. An elastic wave filter having low loss in thepassband, and steep passband characteristics around the passband, isused as the multiple passband filters defining the multiplexer.

International Publication No. 2016/208670 discloses a surface acousticwave device (SAW duplexer) having a configuration in which multiplesurface acoustic wave filters are connected. Specifically, an inductanceelement is connected in series between a connection path to an antennaterminal of a reception-side surface acoustic wave filter and atransmission-side surface acoustic wave filter, and an antenna element,to enable impedance matching between the antenna element and antennaterminal. This inductance element enables complex impedance, whenviewing the surface acoustic wave filter from the antenna terminal towhich multiple surface acoustic wave filters that have capacitance areconnected, to be brought closer to the characteristic impedance. Thus,International Publication No. 2016/208670 describes that deteriorationof insertion loss is able to be prevented.

Regarding connection of a transmission terminal of a transmission-sidesurface acoustic wave filter to a power amplifier (PA) and a receptionterminal of a reception-side surface acoustic wave filter to a low-noiseamplifier (LNA), the characteristic impedance of the transmissionterminal of the transmission-side surface acoustic wave filter and thereception terminal of the reception-side surface acoustic wave filter issometimes designed to match the respective PA and LNA in recent years,in order to reduce the number of matching elements to perform impedancematching. However, the characteristic impedance of the antenna-sideterminal of the transmission-side surface acoustic wave filter and thereception-side surface acoustic wave filter is 50Ω, and therefore, thecharacteristic impedance may be different between the transmissionterminal or the reception terminal side of the surface acoustic wavefilter and the antenna terminal side. The surface acoustic wave deviceand impedance matching method described in International Publication No.2016/208670 is not able to sufficiently match impedance for eachterminal in this case, and there is a problem that insertion lossincreases.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide multiplexer,transmission devices, and reception devices, capable of reducinginsertion loss in the passband of each elastic wave filter, even whenthe characteristic impedance is different between the transmissionterminal or the reception terminal side of the surface acoustic wavefilter and the antenna terminal side.

According to a preferred embodiment of the present invention, amultiplexer that transmits and receives high-frequency signals via anantenna element includes a plurality of elastic wave filters withpassbands different from each other; a common terminal, with which atleast one first circuit element is connected between a connection pathof the common terminal and the antenna element, and a referenceterminal, and at least one second circuit element is connected in seriesto the connection path; and a first inductance element. Each of theplurality of elastic wave filters includes at least one of a seriesresonator connected between an input terminal and an output terminal,and a parallel resonator connected between a connection path connectingthe input terminal and the output terminal, and a reference terminal.Regarding one elastic wave filter of the plurality of elastic wavefilters, one of the input terminal and the output terminal of theelastic wave filter, which is a terminal closer of to the antennaelement, is connected to the common terminal via the first inductanceelement that is connected to the terminal close to the antenna elementand the common terminal, and the terminal close to the antenna elementis connected to the parallel resonator. Regarding the elastic wavefilters other than the one elastic wave filter among the plurality ofelastic wave filters, one of the input terminal and the output terminalof the elastic wave filter, which is a terminal closer of to the antennaelement, is connected to the common terminal, and is connected to theseries resonator.

According to this configuration, freedom in impedance matching isimproved in accordance with the types, characteristics, connectionpositions, and combinations of the first circuit element and the secondcircuit element. Thus, even when the characteristic impedance differsbetween the transmission terminal or the reception terminal of theelastic wave filter side and the antenna terminal side, sufficientimpedance matching is able to be performed for each terminal.Accordingly, insertion loss in the passband of each elastic wave filterof the multiplexer is able to be reduced. Thus, there is no need toprovide a matching element between each elastic wave filter and a PA orLNA, and a high-frequency circuit is able to be provided with a simpleconfiguration.

Impedance of bands other than the band of the one elastic wave filtermay become inductive due to the first inductance element being connectedto the terminal of the one elastic wave filter closer to the antennaelement.

According to this structure, the complex impedance is able to be easilyadjusted to the characteristic impedance using the complex conjugaterelationship. Thus, sufficient impedance matching is able to beperformed for each terminal, even when the characteristic impedancediffers between the transmission terminal or the reception terminal ofthe elastic wave filter side and the antenna side. Accordingly,insertion loss in the passband of each elastic wave filter of themultiplexer is able to be reduced.

The first circuit element or the second circuit element connected to theside closest to the common terminal may be an inductance element.

Accordingly, when the real part of the characteristic impedance whenviewed from the common terminal side is below about 50Ω, and also thecharacteristic impedance of the passband of the multiplexer is in thethird quadrant or fourth quadrant of a Smith chart, the characteristicimpedance is able to be sufficiently matched for each terminal.Particularly, when the real part of the characteristic impedance whenviewed from the common terminal side is below about 50Ω, and also thecharacteristic impedance of the passband of the multiplexer is in thethird quadrant or fourth quadrant of a Smith chart, insertion loss inthe passband of each elastic wave filter of the multiplexer is able tobe reduced.

The first circuit element may be an inductance element, and the secondcircuit element may be a capacitance element, for example.

Accordingly, when the real part of the characteristic impedance whenviewed from the common terminal side is below about 50Ω, and also thecharacteristic impedance of the passband of the multiplexer is in thefourth quadrant of a Smith chart, the characteristic impedance is ableto be sufficiently matched for each terminal. Particularly, when thereal part of the characteristic impedance when viewed from the commonterminal side is below about 50Ω, and also the characteristic impedanceof the passband of the multiplexer is in the fourth quadrant of a Smithchart, insertion loss in the passband of each elastic wave filter of themultiplexer is able to be reduced.

The first circuit element may be a capacitance element, and the secondcircuit element may be an inductance element, for example.

Accordingly, when the real part of the characteristic impedance whenviewed from the common terminal side is below about 50Ω, and also thecharacteristic impedance of the passband of the multiplexer is in thethird quadrant of a Smith chart, and when the real part of thecharacteristic impedance when viewed from the common terminal side isabout 50Ω or above, and also the characteristic impedance of thepassband of the multiplexer is in the third quadrant or fourth quadrantof a Smith chart, the characteristic impedance is able to besufficiently matched for each terminal. Particularly, when the real partof the characteristic impedance when viewed from the common terminalside is below about 50Ω, and also the characteristic impedance of thepassband of the multiplexer is in the third quadrant of a Smith chart,and when the real part of the characteristic impedance when viewed fromthe common terminal side is about 50Ω or above, and also thecharacteristic impedance of the passband of the multiplexer is in thethird quadrant or fourth quadrant of a Smith chart, insertion loss inthe passband of each elastic wave filter of the multiplexer is able tobe reduced.

Of the input terminal and the output terminal of each of the pluralityof elastic wave filters, characteristic impedances of the terminal onthe opposite side from the terminal closer to the antenna element may bedifferent from each other.

Accordingly, the characteristic impedance of each elastic wave filter ofthe multiplexer is able to be adjusted, and therefore, insertion loss inthe passband for characteristic impedance of each elastic wave filter isable to be appropriately reduced.

An elastic wave filter, of the plurality of elastic wave filters, thatneeds isolation from the one elastic wave filter may include a secondinductance element connected in series or in parallel at the terminal onthe opposite side from the terminal closer to the antenna element.

Accordingly, isolation of the elastic wave filter where the secondinductance element is provided is able to be increased by using couplingbetween the second inductance element and the other inductance element.

Complex impedance at a predetermined passband, in a state in which thefirst inductance element and one of the input terminal and the outputterminal of the one elastic wave filter which is the terminal closer tothe antenna element are connected in series, when viewing the oneelastic wave filter alone via the first inductance element, and compleximpedance at the predetermined passband, in a state in which one of theinput terminal and the output terminal of each of the elastic wavefilters other than the one elastic wave filter which is the terminalcloser to the antenna element is connected to the common terminal, whenviewing the elastic wave filters other than the one elastic wave filterfrom the side of the terminal closer to the antenna element andconnected to the common terminal, may be in a complex conjugaterelationship.

Accordingly, complex impedance viewed from the common terminal of themultiplexer including the composited circuit, where the circuit in whichthe first inductance element and one elastic wave filter have beenconnected in series, and the circuit where the elastic wave filtersother than the one elastic wave filter have been connected in parallelat the common terminal, have been composited, is able to be made tomatch the characteristic impedance while securing low loss within thepassband. Connecting the first inductance element in series between thecommon terminal and the antenna element enables fine adjustment of thecomplex impedance of the multiplexer when viewed from the commonterminal to the induction side.

A piezoelectric substrate of each of the plurality of elastic wavefilters may include a piezoelectric film on one surface of which aninterdigital transducer (IDT) electrode is provided, ahigh-acoustic-velocity supporting substrate in which a bulk waveacoustic velocity propagating through the high-acoustic-velocitysupporting substrate is faster than an elastic wave velocity propagatingthrough the piezoelectric film, and a low-acoustic-velocity film that isdisposed between the high-acoustic-velocity supporting substrate and thepiezoelectric film, where a bulk wave acoustic velocity propagatingthrough the low-acoustic-velocity film is slower than a bulk waveacoustic velocity propagating through the piezoelectric film.

Circuit elements, such as an inductance element and capacitance element,may be included to perform impedance matching between the multipleelastic wave filters, such as a case in which the first inductanceelement is connected in series at the common terminal side of the oneelastic wave filter. In this case, a situation is conceivable in whichthe Q values of the resonators are equivalently reduced. However, withthe laminated structure of the piezoelectric substrate, the Q values ofthe resonators are able to be maintained at high values. Accordingly, anelastic wave filter that has low in-band loss is able to be provided.

The multiplexer may include, as the plurality of elastic wave filters, afirst elastic wave filter that has a first passband, and outputstransmission signals to the antenna element, a second elastic wavefilter that has a second passband adjacent to the first passband, andreceives reception signals from the antenna element, a third elasticwave filter that has a third passband on the lower frequency side fromthe first passband and the second passband, and outputs transmissionsignals to the antenna element, and a fourth elastic wave filter thathas a fourth passband on the higher frequency side from the firstpassband and the second passband, and receives reception signals fromthe antenna element, the one elastic wave filter to which the firstinductance element is connected in series being at least one of thesecond elastic wave filter and the fourth elastic wave filter.

According to a preferred embodiment of the present invention, atransmission device receives a plurality of high-frequency signals withcarrier frequency bands that are different from each other, filters theplurality of high-frequency signals, and wirelessly transmits signalsfrom a common antenna element. The transmission device includes aplurality of transmitting elastic wave filters that receive theplurality of high-frequency signals from a transmission circuit, andpass only a predetermined frequency band; and a common terminal, withwhich at least one first circuit element is connected between aconnection path of the common terminal and the antenna element, and areference terminal, and at least one second circuit element is connectedin series to the connection path. Each of the plurality of transmittingelastic wave filters includes at least one of a series resonatorconnected between an input terminal and an output terminal, and aparallel resonator connected between a connection path connecting theinput terminal and the output terminal, and a reference terminal. Anoutput terminal of one of the plurality of transmitting elastic wavefilters is connected to the common terminal via an inductance elementthat is connected to the output terminal and to the common terminal, andthe output terminal is connected to the parallel resonator. An outputterminal of the transmitting elastic wave filters other than the onetransmitting elastic wave filter, is connected to the common terminal,and is connected to the series resonator among the series resonator andthe parallel resonator.

According to a preferred embodiment of the present invention, areception device receives a plurality of high-frequency signals withcarrier frequency bands that are different from each other via anantenna element, demultiplexes the plurality of high-frequency signals,and outputs signals to a reception circuit. The reception deviceincludes a plurality of receiving elastic wave filters that receive theplurality of high-frequency signals from the antenna element, and passonly a predetermined frequency band; and a common terminal, with whichat least one first circuit element is connected between a connectionpath of the common terminal and the antenna element, and a referenceterminal, and at least one second circuit element is connected in seriesto the connection path. Each of the plurality of receiving elastic wavefilters includes at least one of a series resonator connected between aninput terminal and an output terminal, and a parallel resonatorconnected between a connection path connecting the input terminal andthe output terminal, and a reference terminal. An input terminal of oneof the plurality of receiving elastic wave filters is connected to thecommon terminal via an inductance element that is connected to the inputterminal and to the common terminal, and the input terminal is connectedto the parallel resonator. An input terminal of the receiving elasticwave filters other than the one receiving elastic wave filter, isconnected to the common terminal, and is connected to the seriesresonator among the series resonator and the parallel resonator.

According to a preferred embodiment of the present invention, animpedance matching method of a multiplexer that transmits and receives aplurality of high-frequency signals via an antenna element includesadjusting a plurality of elastic wave filters with passbands that aredifferent from each other, such that when viewing one elastic wavefilter from one of an input terminal and an output terminal of the oneelastic wave filter, complex impedance at passbands of other elasticwave filters is in a short state, and when viewing each of the otherelastic wave filters than the one elastic wave filter from one of theinput terminal and the output terminal of each of the other elastic wavefilters alone, complex impedance at passbands of the other elastic wavefilters is in an open state; adjusting inductance values of a filtermatching inductance element such that complex impedance when the filtermatching inductance element is connected in series to the one elasticwave filter, when viewing the one elastic wave filter from the filtermatching inductance element side, and complex impedance when the elasticwave filters other than the one elastic wave filter are connected inparallel to the common terminal, when viewing the other elastic wavefilters from the common terminal side, are in a complex conjugaterelationship; and adjusting, in a compositing circuit in which the oneelastic wave filter is connected to the common terminal via the filtermatching inductance element and the other elastic wave filters areconnected to the common terminal in parallel, at least one first circuitelement connected between a connection path of the antenna element andthe common terminal, and a reference terminal, and at least one secondcircuit element connected in series to the connection path of theantenna element and the common terminal, such that complex impedancewhen viewed from the common terminal matches a characteristic impedance.In the adjusting of the plurality of elastic wave filters, among theplurality of elastic wave filters including at least one of a seriesresonator connected between an input terminal and an output terminal,and a parallel resonator connected between a connection path connectingthe input terminal and the output terminal and a reference terminal, atthe one elastic wave filter, the parallel resonator and the seriesresonator are arrayed so that the parallel resonator is connected to thefilter matching inductance element, and at the other elastic wavefilters, the parallel resonator and the series resonator are arrayed sothat the series resonator, of the parallel resonator and the seriesresonator, is connected to the common terminal.

Accordingly, freedom in impedance matching is improved in accordancewith the types, characteristics, connection positions, and combinationsof the first circuit element and the second circuit element. Thus, evenwhen the characteristic impedance differs between the transmissionterminal or the reception terminal of the elastic wave filter side andthe antenna terminal side, sufficient impedance matching is able to beperformed for each terminal.

With the multiplexers, transmission devices, and reception devicesaccording to preferred embodiments of the present invention, even whenthe characteristic impedance differs between the transmission terminalor the reception terminal of the elastic wave filter side and theantenna terminal side, insertion loss in the passband of each elasticwave filter is able to be reduced.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit configuration diagram of a multiplexer according toPreferred Embodiment 1 of the present invention.

FIGS. 2A through 2C are diagrams schematically representing a resonatorof a surface acoustic wave filter according to Preferred Embodiment 1 ofthe present invention, where FIG. 2A is a plan view and FIGS. 2B and 2Care cross-sectional views.

FIG. 3A is a circuit configuration diagram of Band 25 transmission-sidefilter of the multiplexer according to Preferred Embodiment 1 of thepresent invention.

FIG. 3B is a circuit configuration diagram of Band 25 reception-sidefilter of the multiplexer according to Preferred Embodiment 1 of thepresent invention.

FIG. 3C is a circuit configuration diagram of Band 66 transmission-sidefilter of the multiplexer according to Preferred Embodiment 1 of thepresent invention.

FIG. 3D is a circuit configuration diagram of Band 66 reception-sidefilter of the multiplexer according to Preferred Embodiment 1 of thepresent invention.

FIG. 4 is a schematic plan view illustrating the electrode configurationof a longitudinally coupled surface acoustic wave filter according toPreferred Embodiment 1 of the present invention.

FIG. 5A is a graph comparing transmission characteristics of Band 25transmission-side filter according to Preferred Embodiment 1 of thepresent invention and a comparative example.

FIG. 5B is a graph comparing transmission characteristics of Band 25reception-side filter according to Preferred Embodiment 1 of the presentinvention and a comparative example.

FIG. 5C is a graph comparing transmission characteristics of Band 66transmission-side filter according to Preferred Embodiment 1 of thepresent invention and a comparative example.

FIG. 5D is a graph comparing transmission characteristics of Band 66reception-side filter according to Preferred Embodiment 1 of the presentinvention and a comparative example.

FIG. 6A is a Smith chart representing complex impedance as viewed fromthe transmission output terminal of a Band 25 transmission-side filteralone according to Preferred Embodiment 1 of the present invention.

FIG. 6B is a Smith chart representing complex impedance as viewed fromthe reception input terminal of a Band 25 reception-side filter aloneaccording to Preferred Embodiment 1 of the present invention.

FIG. 6C is a Smith chart representing complex impedance as viewed fromthe transmission output terminal of a Band 66 transmission-side filteralone according to Preferred Embodiment 1 of the present invention.

FIG. 6D is a Smith chart representing complex impedance as viewed fromthe reception input terminal of a Band 66 reception-side filter aloneaccording to Preferred Embodiment 1 of the present invention.

FIG. 7 is a Smith chart representing complex impedance as viewed from acommon terminal of a circuit alone in which all filters other than theBand 25 reception-side filter according to Preferred Embodiment 1 of thepresent invention are connected in parallel at the common terminal, anda Smith chart representing complex impedance as viewed from aninductance element side of a circuit alone in which the Band 25reception-side filter according to Preferred Embodiment 1 of the presentinvention and the inductance element are connected in series.

FIG. 8A is a Smith chart illustrating complex impedance as viewed fromthe common terminal of a circuit in which four filters according toPreferred Embodiment 1 of the present invention are connected inparallel at the common terminal.

FIG. 8B is a Smith chart illustrating complex impedance where fourfilters according to Preferred Embodiment 1 of the present invention areconnected in parallel at the common terminal, and an inductance elementis connected between a connection path of the antenna and the commonterminal, and a reference terminal.

FIG. 9 is a circuit configuration diagram illustrating an example of amultiplexer according to Preferred Embodiment 2 of the presentinvention.

FIG. 10 is a diagram for describing the relationship between compleximpedance as viewed from a common terminal and types and connectionpositions of circuit elements connected between the common terminal andantenna element in the multiplexer according to Preferred Embodiment 2of the present invention.

FIG. 11A is a diagram illustrating an example of a type and connectionposition of a circuit element connected between the common terminal andantenna element in the multiplexer according to Preferred Embodiment 2of the present invention.

FIG. 11B is a diagram illustrating another example of a type andconnection position of a circuit element connected between the commonterminal and antenna element in the multiplexer according to PreferredEmbodiment 2 of the present invention.

FIG. 11C is a diagram illustrating another example of a type andconnection position of a circuit element connected between the commonterminal and antenna element in the multiplexer according to PreferredEmbodiment 2 of the present invention.

FIG. 11D is a diagram illustrating another example of a type andconnection position of a circuit element connected between the commonterminal and antenna element in the multiplexer according to PreferredEmbodiment 2 of the present invention.

FIG. 12 is a circuit configuration diagram illustrating another exampleof a multiplexer according to Preferred Embodiment 2 of the presentinvention.

FIG. 13A is a diagram illustrating the configuration of a multiplexeraccording to Modification 1 of a preferred embodiment of the presentinvention.

FIG. 13B is a diagram illustrating the configuration of a multiplexeraccording to Modification 2 of a preferred embodiment of the presentinvention.

FIG. 14 is an operation flowchart describing a multiplexer impedancematching method according to a preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail below with reference to the drawings. Note that the preferredembodiments described below are each general or specific examples.Values, shapes, materials, components, placements, and connected statesof components, and so forth, illustrated in the following preferredembodiments, are only exemplary, and do not restrict the presentinvention. Components in the following preferred embodiments which arenot included in an independent claim are described as being optionalcomponents. The sizes and proportion of sizes of components illustratedin the drawings are not necessarily precisely to scale.

Preferred Embodiment 1

A quadplexer applied to Band 25 (transmission passband of about 1850 MHzto about 1915 MHz, reception passband of about 1930 MHz to about 1995MHz) and Band 66 (transmission passband of about 1710 MHz to about 1780MHz, reception passband of about 2010 MHz to about 2200 MHz) in the TimeDivision Long Term Evolution (TD-LTE) standard is exemplified inPreferred Embodiment 1 of the present invention.

The multiplexer 1 according to the present preferred embodiment ispreferably a quadplexer in which a Band 25 duplexer and a Band 66duplexer are connected at a common terminal 50.

FIG. 1 is a circuit configuration diagram of a multiplexer 1 accordingto the present preferred embodiment. The multiplexer 1 includestransmission-side filters 11 and 13, reception-side filters 12 and 14,an inductance element 21, the common terminal 50, transmission inputterminals 10 and 30, and reception output terminals 20 and 40, asillustrated in FIG. 1. The multiplexer 1 is connected to an antennaelement 2 at the common terminal 50. An inductance element 31 isconnected between the connection path of the common terminal 50 andantenna element 2, and the ground that is a reference terminal. Acapacitance element 32 is connected in series on the connection path ofthe common terminal 50 and antenna element 2. The inductance element 31is connected closer to the common terminal 50 side than the capacitanceelement 32.

In the present preferred embodiment, the inductance element 31 isequivalent to a first circuit element, the capacitance element 32 isequivalent to a second circuit element, and the inductance element 21 isequivalent to a first inductance element. The inductance element 31 andcapacitance element 32 may be included in the multiplexer 1 or may beexternally attached to the multiplexer 1. A configuration may beprovided in which the capacitance element 32 is connected closer to thecommon terminal 50 side than the inductance element 31.

The transmission-side filter 11 is preferably anon-equilibrium-input/non-equilibrium-output bandpass filter (firstelastic wave filter), for example, that receives transmission wavesgenerated at a transmission circuit (Radio Frequency Integrated Circuit(RFIC) or other suitable circuit, for example) via the transmissioninput terminal 10, filters the transmission waves at the Band 25transmission passband (about 1850 MHz to about 1915 MHz: firstpassband), and outputs to the common terminal 50.

The reception-side filter 12 is preferably anon-equilibrium-input/non-equilibrium-output bandpass filter (secondelastic wave filter), for example, that receives reception waves fromthe common terminal 50, filters the reception waves at the Band 25reception passband (about 1930 MHz to about 1995 MHz: second passband),and outputs to the reception output terminal 20. The inductance element21 is connected in series between the reception-side filter 12 and thecommon terminal 50. Due to the inductance element 21 being connected tothe common terminal 50 side of the reception-side filter 12, theimpedances of the transmission-side filters 11 and 13 and thereception-side filter 14 that have passbands outside of the passband ofthe reception-side filter 12 are inductive.

The transmission-side filter 13 is preferably anon-equilibrium-input/non-equilibrium-output bandpass filter (thirdelastic wave filter), for example, that receives transmission wavesgenerated at a transmission circuit (RFIC or other suitable circuit, forexample) via the transmission input terminal 30, filters thetransmission waves at the Band 66 transmission passband (about 1710 MHzto about 1780 MHz: third passband), and outputs to the common terminal50.

The reception-side filter 14 is preferably anon-equilibrium-input/non-equilibrium-output bandpass filter (fourthelastic wave filter), for example, that receives reception waves fromthe common terminal 50, filters the reception waves at the Band 66reception passband (about 2010 MHz to about 2200 MHz: fourth passband),and outputs to the reception output terminal 40.

The transmission-side filters 11 and 13 and the reception-side filter 14are directly connected to the common terminal 50.

Note that the inductance element 21 is not restricted to being connectedbetween the reception-side filter 12 and the common terminal 50, and maybe connected in series between the reception-side filter 14 and thecommon terminal 50.

The structure of a surface acoustic wave resonator defining thetransmission-side filters 11 and 13 and the reception-side filters 12and 14 will now be described.

FIGS. 2A through 2C are schematic diagrams schematically illustrating aresonator of a surface acoustic wave filter according to the presentpreferred embodiment. FIG. 2A is a plan view, and FIGS. 2B and 2C arecross-sectional views taken along the single-dot dashed line in FIG. 2A.FIGS. 2A through 2C are a schematic plan view and schematiccross-sectional views exemplarily illustrating, out of the plurality ofresonators defining the transmission-side filters 11 and 13 and thereception-side filters 12 and 14, the structure of the series resonatorof the transmission-side filter 11. Note that the series resonator inFIGS. 2A through 2C is illustrated for the purpose of describing atypical structure of the aforementioned plurality of resonators, so thenumber, length, and other parameters, of electrode fingers defining theelectrodes are not restricted to this illustration.

A resonator 100 that defines the transmission-side filters 11 and 13 andthe reception-side filters 12 and 14 includes a piezoelectric substrate5, and comb-shaped interdigital transducer (IDT) electrodes 101 a and101 b.

The pair of IDT electrodes 101 a and 101 b are provided on thepiezoelectric substrate 5 facing each other, as illustrated in FIG. 2A.The IDT electrode 101 a includes a plurality of electrode fingers 110 athat are parallel or substantially parallel to each other, and a busbarelectrode 111 a that connects the plurality of electrode fingers 110 a.The IDT electrode 101 b includes a plurality of electrode fingers 110 bthat are parallel or substantially parallel to each other, and a busbarelectrode 111 b that connects the plurality of electrode fingers 110 b.The plurality of electrode fingers 110 a and 110 b extend in a directionorthogonal or substantially orthogonal to the X-axial direction.

IDT electrodes 54 defined by the plurality of electrode fingers 110 aand 110 b and busbar electrodes 111 a and 111 b preferably have alaminated structure including a close contact layer 541 and a mainelectrode layer 542, as illustrated in FIG. 2B, for example.

The close contact layer 541 is a layer to improve close contact betweenthe piezoelectric substrate 5 and the main electrode layer 542. Anexample of material used for the close contact layer 541 is titanium(Ti). The film thickness of the close contact layer 541 is preferablyabout 12 nm, for example.

An example of a material used for the main electrode layer 542 isaluminum (Al) including about 1% copper (Cu), for example. The filmthickness of the main electrode layer 542 is preferably about 162 nm,for example.

A protective layer 55 covers the IDT electrodes 101 a and 101 b. Theprotective layer 55 is a layer provided to protect the main electrodelayer 542 from the ambient environment, to adjust frequency-temperaturecharacteristics, to improve humidity withstanding capabilities, and soforth, and is preferably a film of which the primary component issilicon dioxide, for example. The thickness of the protective layer 55is preferably about 25 nm, for example.

The materials from which the close contact layer 541, main electrodelayer 542, and protective layer 55 are made are not restricted to theaforementioned materials. Further, the IDT electrodes 54 does notnecessarily have the above-described laminated structure. The IDTelectrodes 54 may be made from, for example, Ti, Al, Cu, platinum (Pt),gold (Au), silver (Ag), palladium (Pd), other suitable metals or alloys,and may include a plurality of laminated articles defined by the abovemetals or alloys. Further, the protective layer 55 is not required.

Next, the laminated structure of the piezoelectric substrate 5 will bedescribed.

The piezoelectric substrate 5 includes a high-acoustic-velocitysupporting substrate 51, a low-acoustic-velocity film 52, and apiezoelectric film 53, as illustrated in FIG. 2C. The structure is suchthat the high-acoustic-velocity supporting substrate 51, thelow-acoustic-velocity film 52, and the piezoelectric film 53 are layeredin this order.

The piezoelectric film 53 is preferably, for example, a 50° Y-cutX-propagation lithium tantalite (LiTaO₃) piezoelectric crystal orpiezoelectric ceramic (a LiTaO₃ monocrystal cut along a face where anaxis rotated about 50° from the Y axis on the X axis is the normal or aceramic, being a monocrystal where surface acoustic waves propagate inthe X-axial direction or a ceramic). The thickness of the piezoelectricfilm 53 is preferably about 600 nm, for example. Note that apiezoelectric film 53 made of a 42° to 45° Y-cut X-propagation LiTaO₃piezoelectric crystal or piezoelectric ceramic is preferably used forthe transmission-side filter 13 and reception-side filter 14, forexample.

The high-acoustic-velocity supporting substrate 51 supports thelow-acoustic-velocity film 52, the piezoelectric film 53, and the IDTelectrodes 54. The high-acoustic-velocity supporting substrate 51further is a substrate in which the acoustic velocity of bulk waves inthe high-acoustic-velocity supporting substrate 51 is faster than theelastic waves of surface waves or boundary waves propagating through thepiezoelectric film 53, functioning to confine surface acoustic waves inthe portion in which the piezoelectric film 53 and low-acoustic-velocityfilm 52 are layered, so as to not leak below the high-acoustic-velocitysupporting substrate 51. The high-acoustic-velocity supporting substrate51 is preferably a silicon substrate, for example, the thickness thereofpreferably being about 200 μm, for example.

The low-acoustic-velocity film 52 is a film in which the acousticvelocity of bulk waves in the low-acoustic-velocity film is slower thanthat of bulk waves propagating through the piezoelectric film 53, and isdisposed between the piezoelectric film 53 and thehigh-acoustic-velocity supporting substrate 51. This structure, and thenature of elastic waves where energy is concentrated in an essentiallylow-acoustic-velocity medium, reduces or prevents leakage of surfaceacoustic wave energy to the outside of the IDT electrodes. Thelow-acoustic-velocity film 52 is a film of which the primary componentis preferably silicon dioxide, for example, and the thickness thereof ispreferably about 670 nm, for example.

According to the above-described laminated structure of thepiezoelectric substrate 5, the Q value in the resonant frequency andanti-resonant frequency is able to be significantly increased ascompared to a structure used heretofore of a single-layer piezoelectricsubstrate. That is to say, a surface acoustic wave resonator with a highQ value is provided, such that a filter having small insertion loss isable to be provided using this surface acoustic wave resonator.

Further, impedance is matched between the plurality of surface acousticwave filters, such as a case of connecting the inductance element 21 inseries for impedance matching to the common terminal 50 side of thereception-side filter 12, such that circuit elements, such as inductanceelements and capacitance elements, for example, are added. Cases areconceivable in which this would equivalently reduce the Q value of theresonator 100. However, even in such cases, the Q value of the resonator100 is able to be maintained at a high value due to the above-describedlaminated configuration of the piezoelectric substrate 5. Accordingly, asurface acoustic wave filter having low in-band loss is provided.

Note that the high-acoustic-velocity supporting substrate 51 may have astructure in which a supporting substrate, and a high-acoustic velocityfilm in which the acoustic velocity of propagating bulk waves is fasterthan the elastic waves of surface waves or boundary waves propagatingthrough the piezoelectric film 53, are laminated. Examples of materialsthat may be used for the supporting substrate in this case includepiezoelectric materials, such as sapphire, lithium tantalite, lithiumniobate, crystal, and other suitable piezoelectric materials, dielectricmaterials, such as various types of ceramics such as alumina, magnesia,silicon nitride, aluminum nitride, silicon carbide, zirconia,cordierite, mullite, steatite, forsterite, and other suitable dielectricmaterials, glass, semiconductors, such as silicon, gallium nitride, andother suitable semiconductors, and resin substrate. Examples ofmaterials that may be used for the high-acoustic-velocity film includealuminum nitride, aluminum oxide, silicon carbide, silicon nitride,silicon oxynitride, diamond-like carbon (DLC) or diamond, mediums ofwhich the above materials are the primary component, mediums of whichmixtures of the above materials are the primary component, and othervarious high-acoustic-velocity materials.

Note that in FIGS. 2A and 2B, λ represents the pitch of the plurality ofelectrode fingers 110 a and 110 b of the IDT electrodes 101 a and 101 b,L represents the overlap width of the IDT electrodes 101 a and 101 b, Wrepresents the width of the electrode fingers 110 a and 110 b, Srepresents the width between the electrode fingers 110 a and 110 b, andh represents the height of the IDT electrodes 101 a and 101 b.

The circuit configuration of the filters will be described below withreference to FIGS. 3A through 4.

FIG. 3A is a circuit configuration diagram of the Band 25transmission-side filter 11 of the multiplexer 1 according to thepresent preferred embodiment. The transmission-side filter 11 includesseries resonators 102 through 105, parallel resonators 151 through 154,and inductance elements 141, 161, and 162 to perform matching, asillustrated in FIG. 3A.

The series resonators 102 through 105 are connected in series to eachother between the transmission input terminal 10 and a transmissionoutput terminal 61. The parallel resonators 151 through 154 areconnected to each other in parallel between contact points of thetransmission input terminal 10, the transmission output terminal 61, andthe series resonators 102 through 105, and reference terminals (ground).The transmission-side filter 11 is preferably a ladder bandpass filter,for example, due to the above-described configuration of the seriesresonators 102 through 105 and parallel resonators 151 through 154.

The inductance element 141 is connected in series between thetransmission input terminal 10 and the series resonator 102, and betweenthe transmission input terminal 10 and the parallel resonator 151. Theinductance element 141 is a second inductance element, and thetransmission-side filter 11 that requires isolation from thereception-side filter 12 to which the inductance element 21 isconnected, which will be described later, includes the inductanceelement 141 connected in series to the transmission input terminal 10 onthe opposite side from the common terminal 50 connected to the antennaelement 2. Note that the inductance element 141 may be connected betweenthe connection path of the transmission input terminal 10 and the seriesresonator 102 and the reference terminal. Providing the inductanceelement 141 enables the isolation of the transmission-side filter 11 tobe increased, by using the coupling of the inductance element 141 andthe other inductance elements 161 and 162.

The inductance element 161 is connected between the contact points ofthe parallel resonators 152, 153, and 154, and the reference terminal.The inductance element 162 is connected between the parallel resonator151 and the reference terminal.

The transmission output terminal 61 is connected to the common terminal50 (see FIG. 1). The transmission output terminal is also connected tothe series resonator 105, and is not directly connected to any of theparallel resonators 151 through 154.

FIG. 3C is a circuit configuration diagram of the Band 66transmission-side filter 13 of the multiplexer 1 according to thepresent preferred embodiment. The transmission-side filter 13 includesseries resonators 301 through 304, parallel resonators 351 through 354,and inductance elements 361 through 363 to perform matching, asillustrated in FIG. 3C.

The series resonators 301 through 304 are connected in series between atransmission input terminal 30 and a transmission output terminal 63.The parallel resonators 351 through 354 are connected in parallel toeach other between contact points of the transmission input terminal 30,the transmission output terminal 63, and the series resonators 301through 304, and reference terminals (ground). The transmission-sidefilter 13 is a ladder bandpass filter due to the above-describedconfiguration of the series resonators 301 through 304 and parallelresonators 351 through 354. An inductance element 361 is connectedbetween the connection point of the parallel resonators 351 and 352 anda reference terminal. An inductance element 362 is connected between theparallel resonator 353 and a reference terminal. An inductance element363 is connected between the transmission input terminal and seriesresonator 301. The inductance element 363 is a second inductanceelement, the same as or similar to the inductance element 141 in theabove-described transmission-side filter 11. The inductance element 363may be connected between the connection path of the transmission inputterminal 30 and the series resonator 301, and the reference terminal.

The transmission output terminal 63 is connected to the common terminal50 (see FIG. 1). The transmission output terminal is also connected tothe series resonator 304, and is not directly connected to any of theparallel resonators 351 through 354.

Note that PA (omitted from illustration), for example, is connected tothe transmission input terminals 10 and 30. The characteristic impedanceof the transmission input terminals 10 and 30 may differ in accordancewith the characteristics of the PA that is connected thereto.

FIG. 3B is a circuit configuration diagram of the Band 25 reception-sidefilter 12 of the multiplexer 1 according to the present preferredembodiment. The reception-side filter 12 preferably includes, forexample, a longitudinally coupled resonator surface acoustic wave unit,as illustrated in FIG. 3B. More specifically, the reception-side filter12 includes a longitudinally coupled filter unit 203, a series resonator201, and parallel resonators 251 through 253.

FIG. 4 is a schematic plan view illustrating the electrode configurationof the longitudinally coupled filter unit 203 according to the presentpreferred embodiment. The longitudinally coupled filter unit 203includes IDTs 211 through 215, reflectors 220 and 221, an input port230, and an output port 240, as illustrated in FIG. 4.

The IDTs 211 through 215 each include a pair of IDT electrodes that faceeach other. IDTs 212 and 214 are positioned with IDT 213 interposedtherebetween in the X direction, and IDTs 211 and 215 are positionedwith IDTs 212 through 214 interposed therebetween in the X direction.The reflectors 220 and 221 are disposed with the IDTs 211 through 215interposed therebetween in the X direction. The IDTs 211, 213, and 215are connected in parallel between the input port 230 and referenceterminal (ground), and the IDTs 212 and 214 are connected in parallelbetween the output port 240 and reference terminal.

It can be seen from FIG. 3B that the series resonator 201 and theparallel resonators 251 and 252 define a ladder filter unit.

The transmission input terminal 62 is connected to the common terminal50 (see FIG. 1) via the inductance element 21 (see FIG. 1). Thetransmission input terminal 62 is also connected to the parallelresonator 251, as illustrated in FIG. 3B.

FIG. 3D is a circuit configuration diagram of the Band 66 reception-sidefilter 14 of the multiplexer 1 according to the present preferredembodiment. The reception-side filter 14 includes series resonators 401through 405, parallel resonators 451 through 454, and an inductanceelement 461 to perform matching.

The series resonators 401 through 405 are connected in series between areception output terminal 40 and a reception input terminal 64. Theparallel resonators 451 through 454 are also connected in parallelbetween contact points of the reception output terminal 40, thereception input terminal 64, and the series resonators 401 through 405,and reference terminals (ground). The reception-side filter 14 is aladder bandpass filter due to the above-described configuration of theseries resonators 401 through 405 and parallel resonators 451 through454. The inductance element 461 is also connected between the connectionpoint of the parallel resonators 451, 452, and 453, and the referenceterminal.

The reception input terminal 64 is connected to the common terminal 50(see FIG. 1). The reception input terminal 64 is also connected to theseries resonator 405, and is not directly connected to the parallelresonator 454, as illustrated in FIG. 3D.

Note that a LNA (omitted from illustration), for example, is preferablyconnected to the reception output terminals 20 and 40. Thecharacteristic impedance of the reception output terminals 20 and 40 maydiffer in accordance with the characteristics of the LNA connectedthereto. Further, the characteristic impedance of the reception outputterminals 20 and 40 and the transmission input terminals 10 and 30 mayeach differ from each other.

The layout configuration of the resonators and circuit elements in thesurface acoustic wave filters that the multiplexer 1 according to thepresent preferred embodiment includes is not restricted to the layoutconfiguration exemplarily illustrated by the transmission-side filters11 and 13 and the reception-side filters 12 and 14 in the presentpreferred embodiment. The layout configuration of the resonators andcircuit elements in the surface acoustic wave filters described abovediffers depending on the bandpass characteristics of the requestedspecifications in each frequency band. Examples of the aforementionedlayout configuration include the number of series resonators andparallel resonators that are arrayed, and selection of the filterconfiguration, such as ladder filter, longitudinally coupled resonator,and so forth.

Examples of the characteristics of the principal portions according to apreferred embodiment of the present invention, of the layoutconfigurations of the resonators and circuit elements in the elasticwave filters included in the multiplexer 1 according to the presentpreferred embodiment preferably are as follows.

(1) The transmission-side filters 11 and 13 and the reception-sidefilters 12 and 14 each include at least one of the series resonator andparallel resonator.

(2) The reception input terminal 62 of the reception-side filter 12,which is one elastic wave filter, is connected to the common terminal 50via the inductance element 21, and also is connected to the parallelresonator 251.

(3) The transmission output terminals 61 and 63 of the transmission-sidefilters 11 and 13 and the reception input terminal 64 of thereception-side filter 14, i.e., of the elastic wave filters excludingthe reception-side filter 12, are each connected to the common terminal50, and of the series resonators and parallel resonators, are connectedto the series resonators 105, 304, and 405.

That is to say, the multiplexer 1 according to the present preferredembodiment includes a plurality of elastic wave filters with passbandsthat are different from each other, the common terminal 50 at which theinductance element 31 is connected between the connection path to theantenna element 2 and the reference terminal and the capacitance element32 is connected in series to the connection path to the antenna element2, and the inductance element 21 that is connected in series between thecommon terminal 50 and the reception input terminal 62 of thereception-side filter 12 that is one elastic wave filter.

Each of the plurality of elastic wave filters includes at least oneseries resonator including IDT electrodes provided on the piezoelectricsubstrate 5 (see FIGS. 2A to 2C) and connected between an input terminaland output terminal, and parallel resonator IDT electrodes provided onthe piezoelectric substrate and connected between a connection pathconnecting an input terminal and output terminal, and a referenceterminal. The reception input terminal 62 of the reception-side filter12, of the plurality of elastic wave filters, is connected to the commonterminal 50 via the inductance element 21, and is also connected to theparallel resonator 251. On the other hand, the transmission outputterminals 61 and 63, and the reception input terminal 64 of thetransmission-side filters 11 and 13 and the reception-side filter 14 areeach connected to the common terminal 50 and connected to the seriesresonators 105, 304, and 405, and are not connected to a parallelresonator.

The inductance element 31 is connected between the connection path ofthe common terminal 50 and antenna element 2, and the referenceterminal, and the capacitance element 32 is connected in series to theconnection path of the common terminal 50 and antenna element 2.Changing the inductance value of the inductance element 31 and thecapacitance value of the capacitance element 32 enables compleximpedance of the multiplexer 1 as viewed from the common terminal 50 tobe moved in two directions of a capacitance side or an induction side,and an open side or a shorted side.

Now, the operation principle of the ladder surface acoustic wave filteraccording to the present preferred embodiment will be described.

For example, the parallel resonators 151 through 154 illustrated in FIG.3A each have a resonant frequency frp and anti-resonant frequency fap(>frp), as resonance characteristics. The series resonators 102 through105 also each have a resonant frequency frs and anti-resonant frequencyfas (>frs>frp), as resonance characteristics. Although the resonantfrequencies frs of the series resonators 102 through 105 are preferablydesigned to be the same or substantially the same, the values do notnecessarily need to be the same or substantially the same. This is alsotrue for the anti-resonant frequencies fas of the series resonators 102through 105, the resonant frequencies frp of the parallel resonators 151through 154, and the anti-resonant frequencies fap of the parallelresonators 151 through 154, in that the values do not necessarily needto be the same or substantially the same.

When constructing a bandpass filter from a ladder configuration ofresonators, the anti-resonant frequency fap of the parallel resonators151 through 154 and the resonant frequency frs of the series resonators102 through 105 are preferably brought into close proximity. Thus,around the resonant frequency frp where the impedance of the parallelresonators 151 through 154 approaches 0 becomes a low-frequency sidestopband. Accordingly, when the frequency rises, the impedance of theparallel resonators 151 through 154 becomes higher around theanti-resonant frequency fap, and the impedance of the series resonators102 through 105 around the resonant frequency frs approaches 0. As aresult, around the anti-resonant frequency fap to the resonant frequencyfrs becomes a signal passband on the signal path from the transmissioninput terminal 10 to the transmission output terminal 61. When thefrequency further rises to around the anti-resonant frequency fas, theimpedance of the series resonators 102 through 105 becomes higher, thusproviding a high-frequency side stopband. That is to say, where theanti-resonant frequency fas of the series resonators 102 through 105 isset outside the passband greatly affects the steepness of attenuationcharacteristics at the high-frequency side stopband.

When high-frequency signals are received from the transmission inputterminal 10 to the transmission-side filter 11, potential differencesoccur between the transmission input terminal 10 and the referenceterminal, which causes the piezoelectric substrate 5 to warp, whichgenerates surface acoustic waves propagating in the X direction. Onlyhigh-frequency signals having the frequency component regarding whichpassing is desired pass through the transmission-side filter 11, due tothe pitch λ of the IDT electrodes 101 a and 101 b and the wavelength ofthe passband generally corresponding to one another.

High-frequency bandpass characteristics and impedance characteristics ofthe multiplexer 1 according to the present preferred embodiment will bedescribed, making comparison with a multiplexer according to acomparative example.

High-frequency bandpass characteristics of the multiplexer 1 accordingto the present preferred embodiment will be described, comparing themwith high-frequency bandpass characteristics of a multiplexer accordingto a comparative example.

In comparison with the multiplexer 1 according to the present preferredembodiment illustrated in FIG. 1, the multiplexer according to thecomparative example is configured with no inductance element 31connected between the connection path of the common terminal 50 andantenna element 2 and the ground which is the reference terminal, and nocapacitance element 32 provided in series at this connection path. Themultiplexer according to the comparative example has a configuration inwhich an inductance element is connected in series between the commonterminal 50 and the antenna element 2.

FIG. 5A is a graph comparing Band 25 transmission characteristics of thetransmission-side filter 11 according to the present preferredembodiment and the comparative example. FIG. 5B is a graph comparingBand 25 transmission characteristics of the reception-side filter 12according to the present preferred embodiment and the comparativeexample. FIG. 5C is a graph comparing Band 66 transmissioncharacteristics of the transmission-side filter 13 according to thepresent preferred embodiment and the comparative example. FIG. 5D is agraph comparing Band 66 transmission characteristics of thereception-side filter 14 according to the present preferred embodimentand the comparative example.

It can be seen from FIGS. 5A through 5D that the insertion loss withinthe passband of the multiplexer 1 according to the present preferredembodiment is better than the insertion loss within the passband of themultiplexer according to the comparative example at the transmissionside and the reception side for Band 25 and at the transmission side andthe reception side for Band 66. It can further be seen that themultiplexer 1 according to the present preferred embodiment satisfiesthe requested specifications within the passband (for example,transmission-side insertion loss of about 2.0 dB or less andreception-side insertion loss of about 3.0 dB or less) at all frequencybands at the transmission side and the reception side for Band 25 and atthe reception side for Band 66.

It can also be seen that the multiplexer according to the comparativeexample does not satisfy the requested specifications within thepassband at the transmission side and the reception side for Band 25.

Thus, according to the multiplexer 1 of the present preferredembodiment, even if the number of bands and the number of modes to behandled are increased, insertion loss within the passband of each filteris able to be reduced.

Impedance matching at the multiplexer 1 will be described below,including the reason why the multiplexer 1 according to the presentpreferred embodiment is able to provide low loss within the passband.

FIGS. 6A and 6B are Smith charts representing complex impedance asviewed from the transmission output terminal 61 of a Band 25transmission-side filter 11 alone and complex impedance as viewed fromthe reception input terminal 62 of a Band 25 reception-side filter 12alone according to the present preferred embodiment. FIGS. 6C and 6D areSmith charts representing complex impedance as viewed from thetransmission output terminal 63 of a Band 66 transmission-side filter 13alone and complex impedance as viewed from the reception input terminal64 of a Band 66 reception-side filter 14 alone according to the presentpreferred embodiment.

With regard to the impedances of the transmission-side filters 11 and 13and the reception-side filter 14 alone, the complex impedance atfrequency bands outside of the passband is designed to be at the openside in the multiplexer 1 according to the present preferred embodiment.Specifically, the complex impedances of out-of-passband region B_(OUT11)of the transmission-side filter 11 to which the inductance element 21 isnot connected in FIG. 6A, out-of-passband region B_(OUT13) of thetransmission-side filter 13 to which the inductance element 21 is notconnected in FIG. 6C, and out-of-passband region B_(OUT14) of thereception-side filter 14 to which the inductance element 21 is notconnected in FIG. 6D, are located at the open side. The resonatorsconnected to the common terminal 50 in the above three filters areseries resonators and not parallel resonators, in order to provide thesecomplex impedance layouts.

On the other hand, the resonator connected to the common terminal 50 inthe reception-side filter 12 to which the inductance element 21 isconnected, is a parallel resonator. Accordingly, the complex impedanceof the out-of-passband region B_(OUT12) of the reception-side filter 12is located at the short side, as illustrated in FIG. 6B. The reason whythe out-of-passband region B_(OUT12) is located at the short side willbe described later.

FIG. 7 is a Smith chart representing complex impedance of a circuitalone where all filters other than the Band 25 reception-side filter 12according to the present preferred embodiment are connected in parallelat the common terminal 50, as viewed from the common terminal 50 (leftside), and a Smith chart representing complex impedance of a circuitalone where the Band 25 reception-side filter 12 according to thepresent preferred embodiment and the inductance element 21 have beenconnected in series as viewed from the common terminal 50 (right side).

It can be seen from FIG. 7 that complex impedance in a predeterminedpassband, in a state in which the inductance element and the inputterminal of the reception-side filter 12 are connected in series, whenviewing the reception-side filter 12 alone via the inductance element21, and complex impedance at the predetermined passband, in a state inwhich, of the input terminals and output terminals of thetransmission-side filters 11 and 13 and reception-side filter 14, thecloser terminal to the antenna element 2 is connected to the commonterminal 50, when viewing the transmission-side filters 11 and 13 andthe reception-side filter 14 from the side of the terminal connected tothe common terminal 50, are substantially in a complex conjugaterelationship. That is to say, compositing the two complex impedancesachieves impedance matching, and the complex impedance of the compositedcircuits is close to the characteristic impedance.

Note that the expression that the complex impedances of two circuits arein a complex conjugate relationship includes a relationship in which thepositive and negative complex components of each of the compleximpedances are reversed, and is not restricted to a case in which theabsolute values of the complex components are equal or substantiallyequal. That is to say, the complex conjugate relationship in the presentpreferred embodiment also includes cases in which the complex impedanceof one of the circuits is located at a capacitive area (the lowersemicircle of the Smith chart) and the complex impedance of the othercircuit is located at an inductive area (the upper semicircle of theSmith chart).

Now, the reason why the complex impedance of the out-of-passband regionB_(OUT12) of the reception-side filter 12 is located at the short sideis to shift the complex impedance of the out-of-passband regionB_(OUT12) (the passband of the transmission-side filters 11, thetransmission-side filter 13, and the reception-side filter 14) to aposition having the above-described complex conjugate relationship bythe inductance element 21, as illustrated in FIG. 6B. The inductancevalue of the inductance element 21 at this time is preferably, forexample, about 5.9 nH.

In a case in which the out-of-passband region B_(OUT12) of thereception-side filter 12 is situated at the open side, theout-of-passband region B_(OUT12) must be shifted to a position at whichthere is the above-described complex conjugate relationship by aninductance element 21 that has a greater inductance value. Theinductance element 21 is connected in series to the reception-sidefilter 12, such that the greater the inductance value is, the poorer theinsertion loss in the passband of the reception-side filter 12 becomes.Accordingly, the inductance value of the inductance element 21 is ableto be maintained small by locating the complex impedance of theout-of-passband region B_(OUT12) at the short side using the parallelresonator 251, as with the reception-side filter 12 according to thepresent preferred embodiment, thus enabling insertion loss in thepassband to be reduced.

FIG. 8A is a Smith chart representing complex impedance, viewing themultiplexer 1 according to the present preferred embodiment from thecommon terminal 50. That is to say, the complex impedance illustrated inFIG. 8A represents the complex impedances of the two circuitsillustrated in FIG. 7 composited, as viewed from the common terminal 50thereof. The complex impedances of the two circuits illustrated in FIG.7 are located so as to be in a mutually complex conjugate relationshipwherein the composited complex impedance of the composited circuits isclose to the characteristic impedance in the four passbands, thusachieving impedance matching.

FIG. 8B is a Smith chart representing complex impedance, viewing fromthe antenna element 2 side, in an arrangement in which the inductanceelement 31 is connected between the connection path of the commonterminal 50 and antenna element 2 and the reference terminal, and thecapacitance element 32 is connected in series at the connection path ofthe common terminal 50 and antenna element 2. The circuit in which twocircuits, located in a mutually complex conjugate relationship, havebeen composited, exhibits complex impedance that is shifted towards thecapacitive side and the open side from the characteristic impedance, asillustrated in FIG. 8A.

On the other hand, by connecting the inductance element 31 between theconnection path of the common terminal 50 and the antenna element 2 andthe reference terminal, and connecting the capacitance element 32 inseries at the connection path of the common terminal 50 and the antennaelement 2, adjusts the complex impedance of the multiplexer 1 as viewedfrom the common terminal 50 to the inductive side and the short side.Note that, preferably, the inductance value of the inductance element 31at this time is about 7.0 nH and the capacitance value of thecapacitance element 32 is about 2.5 pF, for example.

Accordingly, in the transmission-side filters 11 and 13 and thereception-side filters 12 and 14, the characteristic impedance at theinput terminal or output terminal opposite to the input terminal oroutput terminal closer to the antenna element 2 is able to be adjustedin accordance with a PA or LNA connected thereto. Thus, impedancematching at the antenna terminal is able to be easily achieved withoutcomplicating the design of the transmission-side filters 11 and 13 andthe reception-side filters 12 and 14.

The following are features of the multiplexer 1 according to the presentpreferred embodiment.

(1) The inductance element 21 is connected in series between thereception-side filter 12 and the common terminal 50.

(2) The inductance element 31 is connected between the connection pathof the common terminal 50 and the antenna element 2 and the referenceterminal, and the capacitance element 32 is connected in series to theconnection path of the common terminal 50 and the antenna element 2.

(3) The parallel resonator 251 is connected to the reception inputterminal 62 of the reception-side filter 12.

(4) The transmission output terminal 61 of the transmission-side filter11, the transmission output terminal 63 of the transmission-side filter13, and the reception input terminal 64 of the reception-side filter 14,are each connected to the series resonators 105, 304, and 405.

According to this configuration, the complex impedance of the circuitalone in which the inductance element 21 and the reception-side filter12 are connected in series as viewed from the common terminal 50, andthe complex impedance of the circuit alone in which all filters otherthan the reception-side filter 12 are connected in parallel at thecommon terminal 50, are able to be in a complex conjugate relationship.Accordingly, impedance matching with the characteristic impedance iseasily achieved for the complex impedance of the multiplexer 1 includingthe circuit in which the two above-described circuits have beencomposited as viewed from the common terminal 50, while providing lowloss in the passband. Also, by connecting the inductance element 31between the connection path of the common terminal 50 and the antennaelement 2 and the reference terminal, and connecting the capacitanceelement 32 in series to the connection path of the common terminal 50and the antenna element 2, the complex impedance of the multiplexer 1 asviewed from the common terminal 50 is able to be moved in two directionson the Smith chart. For example, the complex impedance of themultiplexer 1 as viewed from the common terminal 50 is able to beadjusted to the inductive side and the short side. Accordingly,impedance matching at the antenna terminal is able to be easily achievedwithout complicating the design of the transmission-side filters 11 and13 and the reception-side filters 12 and 14.

Note that in the present preferred embodiment, a configuration has beenillustrated and described in which, preferably, the inductance element31 is connected between the connection path of the common terminal 50and the antenna element 2 and the reference terminal, and thecapacitance element 32 is connected in series to the connection path ofthe common terminal 50 and the antenna element 2, but any combination ofinductance element and capacitance element may be used for the circuitelement connected between the connection path of the common terminal 50and the antenna element 2 and the reference terminal, and the circuitelement connected in series to the connection path of the commonterminal 50 and the antenna element 2. It is sufficient for at least oneeach to be provided of the circuit element connected between theconnection path of the common terminal 50 and antenna element 2 and thereference terminal, and the circuit element connected in series to theconnection path of the common terminal 50 and the antenna element 2, andtwo or more may be provided.

Preferred Embodiment 2

The multiplexer 1 according to Preferred Embodiment 2 of the presentinvention differs from the multiplexer 1 shown in Preferred Embodiment 1in that the types and connection positions of circuit elements connectedbetween the common terminal 50 and the antenna element 2 differ.

FIG. 9 is a circuit configuration diagram illustrating an example of themultiplexer 1 according to the present preferred embodiment. Themultiplexer 1 illustrated in FIG. 9 includes an inductance element 33connected in series between the common terminal 50 and the antennaelement 2, and a capacitance element 34 connected between the connectionpath of the common terminal 50 and the antenna element 2 and thereference terminal. The inductance element 33 is connected closer to thecommon terminal 50 side than the capacitance element 34.

Now, an optimal combination of types of circuit elements connectedbetween the common terminal 50 and the antenna element 2 and connectionpositions thereof will be described. FIG. 10 is a diagram for describingthe relationship between complex impedance as viewed from the commonterminal 50 in the multiplexer according to the present preferredembodiment, and types of circuit elements connected between the commonterminal 50 and the antenna element 2 and the connection positionsthereof. FIGS. 11A through 11D are diagrams illustrating examples oftypes of circuit elements connected between the common terminal and theantenna element, and the connection positions thereof, in the presentpreferred embodiment. Note that the connection terminal of the antennaelement 2 is represented by terminal 2 a in FIGS. 11A through 11D.

The optimal combination of types of circuit elements connected betweenthe common terminal 50 and the terminal 2 a of the antenna element 2 andthe connection positions thereof depends on the value of the real partof the characteristic impedance of the multiplexer 1 as viewed from thecommon terminal 50, and in which quadrant on the Smith chart thecharacteristic impedance of the high-frequency passband of themultiplexer 1 is located.

In a case in which the real part of the characteristic impedance of themultiplexer 1 is about 50Ω or higher, the combination of the inductanceelement 33 and capacitance element illustrated in FIG. 11A is effectiveif the characteristic impedance in the passband of the multiplexer 1 isin either the third quadrant or the fourth quadrant of the Smith chartillustrated in FIG. 10. In this configuration, preferably, theinductance element 33 is connected in series to the connection path ofthe common terminal 50 (see FIG. 9) of the multiplexer 1 and theterminal 2 a, and the capacitance element 34 is connected between theconnection path of the inductance element 33 and the common terminal 50,and the reference terminal, as illustrated in FIG. 11A.

According to this configuration, the complex impedance as viewed fromthe common terminal is able to be matched to the characteristicimpedance while providing low loss in the passband. In a case in whichthe real part of the characteristic impedance of the multiplexer 1 islower than about 50Ω, the combination of the inductance element 33 andthe capacitance element 34 illustrated in FIG. 11B is effective if thecharacteristic impedance in the high-frequency passband of themultiplexer 1 is in the third quadrant of the Smith chart illustrated inFIG. 10.

In this configuration, preferably, the inductance element 33 isconnected in series to the connection path of the common terminal 50(see FIG. 9) of the multiplexer 1 and the terminal 2 a, and thecapacitance element 34 is connected between the connection path of theterminal 2 a and the inductance element 33, and the reference terminal,as illustrated in FIG. 11B. This configuration is the same as thecombination of circuit elements illustrated in FIG. 9.

Accordingly, the combination and connection positions of the inductanceelement 33 and the capacitance element 34 illustrated in FIG. 9 areeffective if the real part of the characteristic impedance of themultiplexer 1 is lower than about 50Ω as viewed from the common terminal50 side of the multiplexer 1, and the characteristic impedance in thepassband of the multiplexer 1 is in the third quadrant of the Smithchart.

In a case in which the real part of the characteristic impedance of themultiplexer 1 is lower than about 50Ω, and the characteristic impedancein the high-frequency passband of the multiplexer 1 is in the fourthquadrant of the Smith chart illustrated in FIG. 10, the combination ofthe inductance element 31 and the capacitance element 32 illustrated inFIG. 11C, and the combination of the inductance element 31 and theinductance element 33 illustrated in FIG. 11D, are effective.

In this configuration, the capacitance element 32 is connected in seriesto the connection path of the common terminal (see FIG. 9) of themultiplexer 1 and the terminal 2 a, and the inductance element 31 isconnected between the connection path of the common terminal 50 and thecapacitance element 32 and the reference terminal, as illustrated inFIG. 11C. This configuration is the same or substantially the same asthe combination of the inductance element 31 and capacitance element 32illustrated in FIG. 1. Accordingly, the combination and the connectionpoint of the inductance element 31 and the capacitance element 32illustrated in FIG. 1 is effective if the real part of thecharacteristic impedance of the multiplexer 1 as viewed from the commonterminal 50 side is lower than about 50Ω, and the characteristicimpedance in the passband of the multiplexer 1 is in the fourth quadrantof the Smith chart.

A configuration may also be provided in which the inductance element 33is connected in series to the connection path of the common terminal 50(see FIG. 9) of the multiplexer 1 and the terminal 2 a, and theinductance element 31 is connected between the connection path of thecommon terminal 50 and the inductance element 33 and the referenceterminal, as illustrated in FIG. 11D. This configuration is alsoeffective if the real part of the characteristic impedance of themultiplexer 1 as viewed from the common terminal 50 side is lower thanabout 50Ω, and the characteristic impedance in the passband of themultiplexer 1 is in the fourth quadrant of the Smith chart.

Note that the number of the circuit element connected between theconnection path of the common terminal 50 and the antenna element 2 andthe reference terminal, and the circuit element connected in series tothe connection path of the common terminal 50 and the antenna element 2,is not restricted to one each, and two or more may be provided. FIG. 12is a circuit diagram illustrating another example of a multiplexeraccording to the present preferred embodiment.

The multiplexer 1 illustrated in FIG. 12 includes the capacitanceelement 32 connected in series to the connection path of the commonterminal 50 and the antenna element 2. The inductance element 31 also isprovided between the connection path of the common terminal 50 and thecapacitance element 32 and the reference terminal. Further, themultiplexer 1 illustrated in FIG. 12 includes an inductance element 35provided between the connection path of the capacitance element 32 andthe antenna element 2 and the reference terminal.

According to this configuration, two inductance elements 31 and 35 arepreferably provided between the connection path of the common terminal50 and the antenna element 2 and the reference terminal, such that evenfiner adjustment is able to be made. Accordingly, the characteristicimpedance is able to be easily adjusted to the inductive side and theshort side on the Smith chart to match impedance.

Although examples of quadplexers have been described regarding themultiplexers according to preferred embodiments of the presentinvention, the present invention is not restricted to theabove-described arrangements. For example, arrangements in which theabove-described preferred embodiments are modified as follows may beincluded in the present invention.

For example, the piezoelectric film 53 of the piezoelectric substrate 5according to a preferred embodiment of the present invention ispreferably made of a 50° Y-cut X-propagation LiTaO₃ monocrystal, but thecut angle of the monocrystal material is not restricted to this value.That is to say, the cut angle of the piezoelectric substrate of thesurface acoustic wave filters defining the multiplexer according to thepreferred embodiments is not restricted to about 50° Y. The same orsubstantially the same effects and advantages are obtained by surfaceacoustic wave filters made of a LiTaO₃ piezoelectric substrate having acut angle other than that described above.

Also, the multiplexer 1 according to a preferred embodiment of thepresent invention may further include a configuration in which at leastone first circuit element is connected between the connection path ofthe antenna element 2 and the common terminal 50 and the referenceterminal, and at least one second circuit element is connected in seriesto the connection path of the antenna element 2 and the common terminal50. The first circuit element and the second circuit element may each bean inductance element or a capacitance element. For example, themultiplexer 1 according to the present preferred embodiment maypreferably include a plurality of elastic wave filters having theabove-described characteristics, a chip-shaped first inductance element,and the first circuit element and the second circuit element, mounted ona high-frequency substrate.

The inductance element may be a chip inductor, for example, or may bedefined by a conductor pattern on the high-frequency substrate. Thecapacitance element may be a chip capacitor, for example, or may bedefined by a conductor pattern on the high-frequency substrate.

The multiplexer according to the present preferred embodiment is notrestricted to a Band 25+Band 66 quadplexer as in the preferredembodiments.

FIG. 13A is a diagram illustrating the configuration of the multiplexeraccording to Modification 1 of a preferred embodiment of the presentinvention. For example, the multiplexer according to a preferredembodiment of the present invention may be a hexaplexer including sixfrequency bands, applied to a system configuration in which Band 25,Band 4, and Band 30 including transmission band and reception band arecombined, as illustrated in FIG. 13A. In this case, for example, theinductance element 21 is connected in series to the Band 25reception-side filter, and a parallel resonator is connected to thereception input terminal of the Band 25 reception-side filter. Further,series resonators are connected to the terminals of the remaining fivefilters other than the Band 25 reception-side filter, and no parallelresonators are connected thereto. Also, the capacitance element 32 isconnected in series to the connection path of the common terminal andthe antenna element 2, and the inductance element 31 is connectedbetween the connection path of the common terminal and the capacitanceelement 32 and the reference terminal.

FIG. 13B is a diagram illustrating the configuration of the multiplexeraccording to Modification 2 of a preferred embodiment of the presentinvention. For example, the multiplexer according to a preferredembodiment of the present invention may preferably be a hexaplexerincluding six frequency bands, applied to a system configuration inwhich Band 1, Band 3, and Band 7 having transmission band and receptionband are combined, as illustrated in FIG. 13B. In this case, forexample, the inductance element 21 is connected in series to the Band 1reception-side filter, and a parallel resonator is connected to thereception input terminal of the Band 1 reception-side filter. Further,series resonators are connected to the terminals of the remaining fivefilters other than the Band 1 reception-side filter, and no parallelresonators are connected thereto. Also, the capacitance element 32 isconnected in series to the connection path of the common terminal andthe antenna element 2, and the inductance element 31 is connectedbetween the connection path of the common terminal and the capacitanceelement 32 and the reference terminal.

As described above, sufficient impedance matching is able to be achievedfor each of the terminals of multiplexers according to preferredembodiments of the present invention, even when the characteristicimpedance differs between the transmission terminal or the receptionterminal of the surface acoustic wave filter side and the antennaelement side. Accordingly, insertion loss in the passband is able to bereduced even if the number of elastic wave filters is large.

Further, multiplexers according to preferred embodiments of the presentinvention do not need to be configured including a plurality ofduplexers that transmit and receive. For example, multiplexers accordingto preferred embodiments of the present invention may be applied to atransmission device including a plurality of transmission frequencybands. That is to say, multiplexers according to preferred embodimentsof the present invention may be applied to a transmission device thatreceives a plurality of high-frequency signals including carrierfrequency bands that are different from each other, filters theplurality of high-frequency signals, and wirelessly transmits from acommon antenna element. The transmission device may include a pluralityof transmitting elastic wave filters that receive the plurality ofhigh-frequency signals from a transmission circuit, and pass only apredetermined frequency band, and a common terminal, regarding which atleast one first circuit element is connected between a connection pathof the common terminal and the antenna element, and a referenceterminal, and at least one second circuit element is connected in seriesto the connection path of the common terminal and the antenna element.Each of the plurality of transmitting elastic wave filters preferablyincludes at least one of a series resonator including an IDT electrodeprovided on a piezoelectric substrate and connected between an inputterminal and an output terminal, and a parallel resonator including anIDT electrode provided on a piezoelectric substrate and connectedbetween a connection path connecting the input terminal and the outputterminal, and a reference terminal. An output terminal of onetransmitting elastic wave filter of the plurality of transmittingelastic wave filters is connected to the common terminal via aninductance element that is connected to this output terminal and to thecommon terminal, and also is connected to the parallel resonator. On theother hand, an output terminal of the transmitting elastic wave filtersother than the one transmitting elastic wave filter, is connected to thecommon terminal, and also is connected to, of the series resonator andthe parallel resonator, the series resonator. The first circuit elementand the second circuit element may be an inductance element or may be acapacitance element.

Further, multiplexers according to preferred embodiments of the presentinvention may be applied to a reception device including a plurality ofreception frequency bands. That is to say, multiplexers according topreferred embodiments of the present invention may be applied to areception device that receives a plurality of high-frequency signalsincluding carrier frequency bands that are different from each other viaan antenna element, branches the plurality of high-frequency signals,and outputs to a reception circuit. The reception device preferablyincludes a plurality of receiving elastic wave filters that receive theplurality of high-frequency signals from the antenna element, and passonly a predetermined frequency band, and a common terminal, regardingwhich at least one first circuit element is connected between aconnection path of the common terminal and the antenna element, and areference terminal, and at least one second circuit element is connectedin series to the connection path of the common terminal and the antennaelement. Each of the plurality of transmitting elastic wave filtersincludes at least one of a series resonator including an IDT electrodeprovided on a piezoelectric substrate and connected between an inputterminal and an output terminal, and a parallel resonator including anIDT electrode provided on a piezoelectric substrate and connectedbetween a connection path connecting the input terminal and outputterminal, and a reference terminal. An input terminal of one receivingelastic wave filter of the plurality of receiving elastic wave filtersis connected to the common terminal via an inductance element that isconnected to this input terminal and to the common terminal, and also isconnected to the parallel resonator. On the other hand, an inputterminal of the receiving elastic wave filters other than the onereceiving elastic wave filter, is connected to the common terminal, andalso is connected to, of the series resonator and the parallelresonator, the series resonator. The first circuit element and secondcircuit element may be an inductance element or may be a capacitanceelement.

A transmission device or a reception device having the configurationdescribed above is able to obtain the same or substantially the sameadvantages as the multiplexer 1 according to the preferred embodimentsof the present invention.

Preferred embodiments of the present invention also are not restrictedto multiplexers, transmission devices, and reception devices providedwith the elastic wave filters and inductance elements having thefeatures described above, and also may include an impedance matchingmethod of a multiplexer, having the following steps as componentsincluding such features.

FIG. 14 is an operational flowchart for describing an impedance matchingmethod of a multiplexer according to a preferred embodiment of thepresent invention.

An impedance matching method of a multiplexer according to the presentpreferred embodiment includes (1) adjusting a plurality of elastic wavefilters with passbands that are different from each other, such thatwhen viewing one elastic wave filter (elastic wave filter A) from one ofthe input terminal and the output terminal of the one elastic wavefilter, complex impedance at passbands of other elastic wave filters(elastic wave filters B) is in a shorted state, and when viewing elasticwave filters other than the one elastic wave filter from one of theinput terminal and the output terminal of the other elastic wave filtersalone, complex impedance at passbands of the other elastic wave filtersis in an open state (S10), (2) adjusting inductance values of a filtermatching inductance element such that complex impedance when the filtermatching inductance element is connected in series to the one elasticwave filter (elastic wave filter A), when viewing the one elastic wavefilter from the filter matching inductance element side, and compleximpedance when elastic wave filters (multiple elastic wave filters B)other than the one elastic wave filter are connected in parallel to thecommon terminal, when viewing the other elastic wave filters from thecommon terminal side, are in a complex conjugate relationship (S20), and(3) adjusting, in a compositing circuit in which the one elastic wavefilter (elastic wave filter A) is connected to the common terminal viathe filter matching inductance element and the other elastic wavefilters (multiple elastic wave filters B) are connected to the commonterminal in parallel, at least one first circuit element connectedbetween a connection path of the antenna element and the commonterminal, and a reference terminal, and at least one second circuitelement connected in series to the connection path of the antennaelement and the common terminal, such that complex impedance when viewedfrom the common terminal matches a characteristic impedance (S30).

The first circuit element and second circuit element are each preferablyan antenna matching inductance element or an antenna matchingcapacitance element, for example. In this case, adjustment of the firstcircuit element and the second circuit element may be adjustment of theinductance value of the antenna matching inductance element andadjustment of the capacitance value of the antenna matching capacitanceelement. Further, adjustment of the first circuit element and the secondcircuit element may include changing types, characteristics, connectionpositions, and combination, for example, of the first circuit elementand the second circuit element.

Further, in the adjusting of the plurality of elastic wave filters, ofthe plurality of elastic wave filters including at least one of a seriesresonator including an IDT electrode provided on a piezoelectricsubstrate and connected between an input terminal and an outputterminal, and a parallel resonator including an IDT electrode providedon a piezoelectric substrate and connected between a connection pathconnecting the input terminal and the output terminal and a referenceterminal, at the one elastic wave filter, the parallel resonator and theseries resonator are arrayed with the parallel resonator connected tothe filter matching inductance element, and at the other elastic wavefilters the parallel resonator and the series resonator are arrayed withthe series resonator connected to the common terminal.

According to this configuration, freedom in impedance matching is ableto be improved by adjusting the first circuit element and the secondcircuit element as described above. Thus, even when the characteristicimpedance differs between the transmission terminal or the receptionterminal of the elastic wave filter side and the antenna terminal side,sufficient impedance matching is able to be performed for each terminal.

Surface acoustic wave filters including IDT electrodes have beenexemplified in the preferred embodiments described above as atransmission-side filter and a reception-side filter defining amultiplexer, a quadplexer, a transmission device, and a receptiondevice. However, the filters defining the multiplexers, the quadplexers,the transmission devices, and the reception devices according topreferred embodiments of the present invention may be elastic wavefilters using elastic boundary waves or bulk acoustic waves (BAW)including series resonators and parallel resonators. Accordingly, thesame or substantially the same advantages as those of the multiplexers,the quadplexers, the transmission devices, and the reception devicesaccording to the above-described preferred embodiments are able to beobtained.

Also, while the multiplexer 1 according to the above-described preferredembodiments has been exemplarily illustrated as a configuration in whichthe inductance element 21 is connected in series to the reception-sidefilter 12, configurations in which the inductance element 21 isconnected in series to the transmission-side filters 11 or 13 or thereception-side filter 14 are also included in the present invention.That is to say, the multiplexers according to preferred embodiments ofthe present invention may include a plurality of elastic wave filterswith passbands different from each other, a common terminal, regardingwhich at least one first circuit element is connected between aconnection path of the common terminal and the antenna element, and areference terminal, and at least one second circuit element is connectedin series to the connection path of the common terminal and the antennaelement, and a first inductance element, in which, of the plurality ofelastic wave filters, a transmission-side filter includes an outputterminal connected to the common terminal via the first inductanceelement connected to this output terminal and the common terminal, andalso connected to a parallel resonator, and elastic wave filters otherthan the transmission-side filter include, of their input terminal andoutput terminal, the terminal toward the side of the antenna elementconnected to the common terminal, and also connected to, of a seriesresonator and a parallel resonator, a series resonator. Thus, even whenthe characteristic impedance differs between the transmission terminalside or the reception terminal side of the elastic wave filter and theantenna terminal side, sufficient impedance matching is able to beperformed for each terminal. Accordingly, a low-loss multiplexer is ableto be provided even if the number of bands and the number of modes to behandled are increased.

Preferred embodiments of the present invention are broadly applicable tocommunication devices, such as cellular phones, as a low-lossmultiplexer, a transmission device, and a reception device applicable tomulti-band and multi-mode frequency standards.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A multiplexer that transmits and receives high-frequency signals via an antenna element, the multiplexer comprising: a plurality of elastic wave filters with passbands different from each other; a common terminal; a first inductance element connected in series between the common terminal and one elastic wave filter of the plurality of elastic wave filters; a second inductance element connected between the antenna element and the common terminal; wherein each of the plurality of elastic wave filters includes: a series resonator connected between an input terminal and an output terminal; and a parallel resonator connected between a connection path connecting the input terminal and the output terminal and a reference terminal; in the one elastic wave filter of the plurality of elastic wave filters, one of the input terminal and the output terminal of the one elastic wave filter that is closer to the antenna element is connected to the common terminal via the first inductance element, and the one of the input terminal and the output terminal closer to the antenna element is connected to the parallel resonator; and in each of the plurality of elastic wave filters other than the one elastic wave filter, one of the input terminal and the output terminal of the elastic wave filter that is closer to the antenna element is connected to the common terminal and to the series resonator.
 2. The multiplexer according to claim 1, wherein in one of the plurality of elastic wave filters other than the one elastic wave filter, a third inductance element is connected between the series resonator and the input terminal or the output terminal opposite to the one of the input terminal and the output terminal closer to the antenna element.
 3. The multiplexer according to claim 2, wherein in one of the plurality of elastic wave filters other than the one elastic wave filter, a fourth inductance element is connected between the parallel resonator and the reference terminal.
 4. The multiplexer according to claim 1, wherein the second inductance element is connected in series between the antenna element and the common terminal.
 5. The multiplexer according to claim 1, wherein at least one of the plurality of elastic wave filters includes a plurality of parallel resonators connected between the connection path and the reference terminal.
 6. The multiplexer according to claim 5, wherein in the at least one of the plurality of elastic wave filters that includes the plurality of parallel resonators, at least two of the plurality of parallel resonators are connected at a common contact point, and a third inductance element is connected between the common contact point and the reference terminal.
 7. The multiplexer according to claim 1, wherein the one elastic wave filter is a reception filter for Band
 25. 8. The multiplexer according to claim 1, wherein one of the plurality of elastic wave filters other than the one elastic wave filter is a transmission filter for Band
 25. 9. The multiplexer according to claim 1, wherein one of the plurality of elastic wave filters other than the one elastic wave filter is a transmission filter for Band
 66. 10. The multiplexer according to claim 1, wherein one of the plurality of elastic wave filters other than the one elastic wave filter is a reception filter for Band
 66. 